Using cosmetics to lighten skin is NOT the same as trying to "heal blackness". White people often darken their skin with chemicals (sunless tanning). This is NOT because they don't want to be white, or because they are trying to "heal whiteness". This is just a cosmetic change. In the United States at least, blackness is a boolean data type. You either are black or not. Being 25% black=Black all the way. Lightening skin is not about decreasing blackness.

Nobody says blackness is an illness now, because you cannot change it. If it ever became easily changeable, that would change very quickly.

Not a chance. Deaf people face all sorts of real world challenges and discrimination, but they often don't cure their deafness (say, with cochlear implants) because they feel a sense of comraderie. Black people would face overwhelming social scorn if they chose to become white. Black people who are considered even slightly